electrocardiographic effect
a change in the electrical activity of the heart as recorded by an electrocardiogram, especially a change associated with administration of a drug. Prolongation of segments of the cardiac cycle, particularly the Q-T interval (the period of ventricular contraction), may be observed with excess doses of numerous antipsychotics and tricyclic antidepressants. A malignant form of electrocardiographic change is an arrhythmia known as torsades de pointes (French, literally: “twisting of the points”), so called because of its characteristic outline on an electrocardiograph tracing. Torsades de pointes syndrome may result from drug interactions increasing the serum concentration of certain drugs or from an abnormal reaction to single drugs (e.g., pimozide) in susceptible individuals.